Studies in this grant are designed to determine how specific stimulation of renal vasopressin Vl receptors can influence the distribution of renal blood flow, sodium and water excretion, urine concentration, and the long-term level of arterial pressure. We will study the effects of acute renal artery and medullary interstitial infusions of arginine vasopressin (AVP), a Vl receptor agonist, and a Vl antagonist on the distribution of renal blood flow and the relationship of such changes on sodium and water excretion. These studies will use techniques including implanted optical fibers for laser-Doppler flowmetry to determine changes of cortical and medullary flow and fluorescent videomicroscopy and servonull pressure measuring techniques to study vasa recta hemodynamics. Other studies utilizing optical fibers chronically implanted in the cortex and medulla will determine the effects of endogenous AVP secretion on the distribution of renal blood flow during dehydration and over-hydration in unanesthetized rats. Instrumented awake rats also will be used to study long-term changes of renal medullary and cortical blood flow, arterial pressure and cardiac output associated with development of hypertension using a new model produced by the long-term infusion of a Vl receptor agonist into the renal medullary interstitial space.